Apparatus and method for removing scale from liquid evaporation surfaces



Jan. 12, 1932.

A. DAVIS, JR

APPARATUS AND METHOD FOR REMOVING SCALE FROM LIQUID EVAPORATION SURFACESFiled Jan. 29, 1929 3 Sheets-Sheet Jan. 12, 1932. A. H. DAVIS, JR1,840,834

APPARATUS AND METHOD FOR REMOVING SCALE FROM LIQUID EVAPORATION SURFACESFiled Jan. 29, 1929 3 Sheets-Sheet 2 INVIENTOR WM H w) WW Jan. 12, 1932.

A. H. DAVIS, JR 1,840,834

APPARATUS AND METHOD FOR REMOVING SCALE FROM LIQUID EVAPORATION SURFACESFiled Jan. 29, 1929 3 Sheets-Sheet 3 I 27 T r 36 I 57 I fis as INVENTORPatenteddan; 12, 1932 AROHIBALD H. DAVIS, .13., or PITTSBURGH,PENNSYLVANIAJASSIGNOR r SHAW- PERKINS MANUFACTURING COMPANY, OF

PORATION or PENNSYLVANIA APPARATUS AND METHOD FOR PITTSBURGH,PENNSYLVANIA, A COR- REMOVING SCALE FROM LIQUID EVAPORATION SURFACES 7Application filed January 29, 1929. Serial No. 335,785.

This invention relates to the removal of scale from heat-exchangingsurfaces, and

1 especially to its removal from the tubes of liquid evaporationapparatus.

The removal .of scale from the tubes water tube boilers, heating andcooling coils used in chemical processes, and similar apparatus isnecessary for eflicient operation because the scale reduces the rate ofheat transfer and thus decreases evaporation capacity. Heretofore, scalehas usually been removed by scraping the surfaces Wlth, a mechanicalcleaner, or in some cases by means of a vibrating hammer applied to thetubes. All of such means have involved cleaning one tube at a time, andconsequently scale removal has been a tedious and timeconsumingprocedure Furthermore, it has been necessary to design such apparatus sothat all of the heat-exchanging surfaces were accessible, which in someinstances increases construction costs and may be otherwise undesirable.L

An object of this invention is to provide a method of removing scalefrom heat-exchanging surfaces which is eflicient, simple,

rapid, involves no complications in apparatus design, causessimultaneous cleaning of the entire scaled surface decreases cleaningcosts, and makes possible more frequent cleaning of the apparatus.

Another object is to provide liquid evaporation apparatuses similar tothose now in use in which'the heat-exchanging surfaces are miodified toprovide for simultaneous cleaning of .the entire surface, in which theapparatus may be cleaned without being taken out of service, and inwhich the modification does not in any way interfere with the operationof the apparatus.

' Still another object is to provide tubular liquid evaporationapparatus of the type referred to in which no provision need be made foraccess to the individual tubes.

The invention is illustrated in the accompanying drawings, in which Fig.1 is a vertical elevation of an evaporator embodying the invention,parts being broken away for clarity of illustration; Fig. 2 isa'fragnienof evaporators, hot water heaters, fire and tary cross sectionthrough the tube radiator, taken on line II-II, Fig. 1; Fig. 3 is anelevation of another form of evaporator showing a modification of theinvention; Fig. 4 is a vertical sectionthrough one form of rotary valveadapted to be used in the practice of the invention; and Fig. 5 is ahorizontal section of the valve taken on line 1 The invention isapplicable to liquid evaporation apparatus comprising tubular heatexchanging elements, and to heating and cooling elements used withchemicals, v

for example in crystallization apparatus. In the usg of apparatus of thegeneral types mentioned the tubes become incrusted by solids depositedby the liquid. Although it is of value in any heat exchanging device inwhich scale forms-on one side of the heating surface, it is especiallyadapted for use with evaporators, and will be described in itsapplication thereto.

Fig. 1 conventionally shows a form of evaporator comprising acylindrical shell 1, liquor inlet 2, vapor outlet 3, and bottom draw-oil4 through which solids formed in concentration ofthe' liquor, or theconcentrated liquor itself, may be withdrawn. Heat for evaporation issupplied from a fluid passed'through tubes horizontally disposed inside.of the shell in contact with the liquid. In the prior forms (ofapparatus tubes circular in section have been used, but

in accordancewith this invention, these heatexchanging tubes are ofnon-circular cross section, and preferably they are elliptical, orflattened ellipses.

The tubes may be mounted in any suitable or desired manner, .for examplein tube sheets in accordance with the customary practice. It ispreferred, however, to use a radiator of the type disclosed in UnitedStates Patent No. 1,320,652 to C. Sonneborn, dated November 4, 1919.According to that patent, the ends of oval tubes5 are welded topan-shaped, headers 6 having a peripheral flange 7 to which isconnected, preferably by. welding, a similar header section 8, as shownin Fig. 1. One of header sections 8 is connected to .a steam line 9, andthe other is connected to a pipe 10 leading to a steam trap 11. Otherheating fluids than steam may, of course, be used. In the use of thisapparatus, any scale deposited by the liquid forms on the outside oftubes 5.

According to the invention, the scale is removed by simultaneouslydistorting the section of all of the tubes. Preferably this isaccomplished by creating pressure pulsations in a fluid, such as steam,or water, inside the tubes. This operation flexes the walls of thetubes, causing them to change their sectional form, and causes the scaleto flake oil.

The intermittent variation in fluid pressure may be accomplished by avariety of means.

For example, a water hammer may be created in the tubes. They may beflooded and supplied with water from a reciprocating pump without an airchamber, or the water hammer may be produced in other ways available tothose skilled in the'art.

t is preferred however, to accomplish the flexing in the manner shown inFig. 1. @utlet ipe 10 is provided with a branch 12 for disc arging watersupplied to the radiator from a water line 13 connected to inlet 9. Thetubes are flooded with water under pressure, and the water pressuremaintained while a discharge valve is intermittently opened and closed.Preferably a valve 14 disposed in line 12 and driven by a motor 15 isused. in this manner the pressure of the water is relieved when thevalve opens, and is built up as it closes, thus producing a pulsatingfluid pres- I sure within the tube which flexes the walls suflicientlyto thoroughly and rapidly break oil the scale.

The amount of scale deposited will depend upon the character of liquidbeing evaporated and the interval between cleaning steps, and itsadherence will also be eflected by these factors. For this reason it maybe desirable to regulate the intensity of tube vibration, and thisis inpart dependent upon the velocity of the water supplied from line 13. Bymaking this line of considerable length, the water flowing into thetubes reaches them at high velocity, and the eflect is greater than whenwater at low velocity is used. The intensity of tube flexing may thus bevaried by adjusting the length of pipe 13,and it may also be done byproviding an adjustable orifice 16, of any suitable type in line 12intermediate the radiator and valve the maximum flow. of water when thevalve is wide open, and in this manner the force of the pulsations isreadily regulable.

Another form of evaporator is shown in Fig. 3, in which a tube basketcomprising elliptical tubes 5a connected to tube sheets or headers 20,is disposed in the shell 1:; with the tubes vertical, a large centraltube providing the usual downcomer 21 to assist in circulation ofliquid. In this form, steam from line 9a circulates around the tubes,the

14. The orifice limits liquid circulating up through the tubes, and thenreversely through the downcomer. The inside of the tubes becomes sealedin this apparatus.

As in the preceding apparatus, steam is discharged to a trap 11a throughan outlet 10a. The scale formed on the tubes may be removed as before bypulsations in water supplied from a line 13a, caused by opening closingthe motor-operated valve 1%. both this and the preceding case thepressure pulsations are applied to the unsealed side of the tubes, butin this case that is the exterior of the tubes.

lln some instances it may be desirable or necessary to apply thepressure against the scaled side. This may be accomplished by theapparatus shown in Fig. 3 as follows. Water from a line 22 is passedinto the bottom of the evaporator through an intermittently opened valve23 and pipe 24. In the apparatus shown, the upper ends of the tubescannot conveniently be sealed, and the most suitable manner ofpulsatingly flexing the tubes is to vary the velocity of water flowingthrough them, so as to utilize the inertia oi the water head to hold thepressure for an instant while the tube walls are being distorted.

in this modification, the inertia of the mass of water in the apparatusmomentarily opposes pressure applied to it when the pressure is appliedquickly, with blow-like force, to give a sort of water hammer eflect andproduce the desired tube-flexing impulses. H the water is passedintermittently to the apparatus through anordinary valve, an appreciableinterval is necessary each time the valve opens, before the water flowcomes up to maximum velocity. This lag is such that the pressure isapplied relatively slowly to the water in the apparatus and does notcause tube-flexing pulsations. To overcome this lag eiiect of ordinaryvalves, and to rapidly supply water at high velocity to the apparatus,it is preferred to use a three-way rotary valve in which the flow ofwater is constant, the direction of flow through the side arms beingreversed in such manner that the water always is at maximum velocity. Inthis manner, water, at full velocity is intermittently applied to theapparatus in such manner as to produce the pulsations which distort thetube section.

A suitable valve of this type is that shown at 23, Fig. 3, and on anenlarged scale in Figs. 4 and 5. This valve comprises a flan ed crossmounted in the position shown in h i 3. The horizontal arms areconnected to the evaporator intake 24 and to a discharge line I 25, andone of the vertical arms is connected to water supply line 22. A fixedsleeve 26 having ports'27 leading to the side arms is mounted Within thecross, as shown in Figs. 4.- and 5. Mounted for rotation within the r 14and 14a.

sleeve is a valve member 28 comprising a cylinder having ports 29 whichpermit water to flow alternately through ports 27 to lines24 and 25, butso .rranged as to provide substantially continuous flow. The valve iskeyed to a shaft 30 disposed in the other vertical arm and connected toshaft 31 of a motor, not shown. .Suitable bearings, packing glands andthe like are stood.

The resultant effect of this means of removing scale is similar to thatdescribed hereinabove. Water is admitted to pipe 22 and valve 23 isrotated rapidly. Water from the valve alternately enters the evaporatorthrough one port of the valve and asses to waste through the other port.en the tubes have become filled, the pressure of water entering theapparatus isapplied inside them, causing pulsating distortion of thetubes. The valve is designed so that water from line 22 flowscontinuously. That is, at the instant when one port closes, the otheropens, and at no time is the flow of water out off. Consequently, thewater flowing through both ports is always at maximum velocity and thereis no lag of the type referredto above. In this manner, when the portleading to the evaporator opens, the high velocity of the water causesapplication of pressure so suddenly to that in the apparatus, that thereis no time for it to be absorbed, and consequently, pulsation results.As in the preceding modification, it is desirable to make water line 22of considerable length, so that the water enters the valve at itshighest velocity.

The valve just described maybe modified to vary the effects produced,and the same general type of valve may be used for valves In the lattercase, a T could be used, the connection to an external source of waterbeing unnecessary. I V In the form of apparatus just described, theremay be greater distorting tendenc at the lower ends of the tubes,especially w ere the tubes are long. Although very slight vibration ofthe tube walls will usually be effective, it may be desirable tocreateuniform dis.v

tortion throughout the tubes. This may be accomplished by increasing theratio of the a major to the minor axes of the tube section progressivelyfrom the bottom to the top. This gradual flattening of the tube thenproduces uniform pressure distribution.

, The invention is, of course, applicable to other forms of liquidevaporation apparatus, such as boilers. Various other means ofpulsatingly-deforming the tubes inay also be employed, since pressurepulsations in a fluid may be set up in a number of ways. Also, pulsatingfluids other than water may be made use of. Thus, steam may be passedinto tubes flooded with water, or pulsating air pressure may be used.

provided, as will be underthere being no need for access to theindivid-.

ual tubes, apparatus may be designed for greater efliciency or atlower-construction costs. All of these factors combine to give greaterevaporating capacity and lower operatingcosts, and the inventiongoes'far to eliminate the prior disadvantages and difli- 'culties whichattended the removal of scale from liquid evaporation apparatus. Iclaim:

1. In a liquid evaporation apparatus, the combination of tubular membersof non-cir: cularv cross section for conducting heat applied on one sideof the tubes to a liquid in contact with the other, and means forrepeatedly applying changing hydrostatic pressure to one side of thetubes to distort the tube section substantially simultaneously along thelength thereof.

2. In a liquid evaporation apparatus, the

combination of tubular members of non-circular cross section forconducting heat applied on'one side of the tubes to a liquid in contactwith the other, and means 'for applyingpulsating fluid pressure to oneside of the tubes to remove scale deposited by the m0 liquid.

3. In a liquid evaporation apparatus, the combination of tubular membersof elliptical cross section for supplying heat from a fluid on one sideof the tubes to a liquid in contact with the other, and means forremoving scale deposited on the tubes comprising means for'intermittently varying the pressure of .a fluid in contact with theunsealed side of the tubes. 4. In a liquid evaporation apparatus, thecombination of a radiator comprising head ers and a plurality of tubesof non-circular cross section connecting the headers, connections forsupplying aheating fluid to one side of all of the tubes, connectionsforsupplying a liquid to be evaporated to the other side, and pulsatingmeans for causing the tubes to change section.

5. In an evaporator, the combination of a radiator comprising tubes ofnon-circular cross section, steam inlet and discharge connections to oneside of the tubes, a connection for supplying liquid to be evaporated tothe other side of the tubes, and scale-removing means associated withone of said connections .comprisingmeans for supplying a fluid to onecross section, steam inlet and discharge conscaled walls of the tubes toflex the walls rapnections to-one side of the tubes, a connecidly bychanging hydrostatic pressure and tion for supplying liquid to beevaporated cause them'to change in sectional form.

to the other side of the tubes, a valve in one In testimony whereof, Isign my name.

5 of said connections, and means for supply- ARCHIBALD H. DAVIS, JR.

ing Water under pressure through said valve to the tubes, and a motoradapted to intermittently open and close the valve whereby topulsatingly vary the pressure of the water on the tubes. 75

7. In an evaporator, the combination of a radiator comprising tubes ofelliptical cross section, steam inlet and discharge connections to oneside of the tubes, a connection to the other side of the "tubes forsupplying liquid 80 to be evaporated, a motor-operated rotary valve inone of the connections, and means for supplying water under pressure tothe valve, intermittent opening and closing of the valve, applyingpulsating pressure to the 85 unscaled side of the tubes whereby toremove scale deposited by the liquid.

8. In an evaporator, the combination of a radiator comprising tubes ofelliptical cross section, steam inlet and discharge connections to oneside of the tubes, a connection to the other side of the tubesfor-supplying liquid to be evaporated, a motor-operated threeway valveconnected to a source of water hav- 30 ing one port connected to oneside of the 95 tubes and another port connected to a waste line, theflow of water through said valve being continuous but alternated betweensaid ports to cause pulsating distortion of the tube walls. I

9. The method of removing scale from heat-exchanging tubes ofnon-circular cross section comprising placing a fluid in contact withthe tubes, and creating pulsating pres- 40 sure waves in the fluid tovary its pressure 105 on the tube walls.

10. The method of removing scale from heat-exchanging tubes ofnon-circular section comprising filling the space on one side of thetubes with a fluid under pressure, and 110 intermittently varying thepressure on the fluid to pulsatingly flex the tube walls.

11. The method of removing scale from heat-exchanging tubes ofelliptical section comprising filling the space on the unsealed side ofthe tubes with water under pressure, and intermittently varying thepressure on the water to pulsatingly flex the tube walls.

12; A method of removing scale from heat- 120 exchanging tubes ofnon-circular cross section comprising rapidly repeatedly creating achanging pressure difi'erence on opposite sides of the tubes to causethem to change in crosssectional form substantially simultaneously alongthe length thereof.

13. A method of removing scale from substantially straightheat-exchanging tubes of non-circular cross section comprisingrepeatedly abruptly applying a fluid to the un- 130

